Hydraulic pumps and motors of the piston type utilize a plurality of axially extending pistons and associated cylinders and a yoke engaged by the pistons and pivoted by annular bearings in a housing.
In another type of hydraulic pump or motor, the bearing form is that of a partial journal bearing often termed a "saddle bearing". The use of this bearing form gives the advantage of a reduction in overall size and in utilizing fewer parts in the bearing area thereby making it more reliable, easier to maintain, involving less deflection on the yoke. The saddle bearing can be either a rolling element or a non-rolling element bearing format. This invention deals with a non-rolling element form of saddle bearing.
In hydraulic pumps and motors journal bearings generally function through hydrodynamic, hydrostatic or hybrid oil filmgeneration processes. There are, however, circumstances when normal lubrication mechanics are insufficient to correctly form a fluid film for the journal bearing to function, typical cases are extreme load, quasi-steady state operation or poor lubrication. Such is the case with a non hydrostatic form of a saddle bearing. Under these circumstances surface to surface contact can and does occur with resulting high coefficients of friction and wear rates. In an attempt to overcome this problem a self lubricated material is used for one of the surfaces in contact. Self lubricated bearings, thus formed however, do have limitations; temperature, load, speed of operation, etc. Many of the self lubricated bearing forms utilize a polymer as the self lubricated material. While these polymers impart a low coefficient of friction for the bearing pair they have a relatively low load capacity due to the yield strength of the polymer. Other materials possessing a higher yield strength cannot achieve a suitably low coefficient of friction. Attempts have been made to increase the yield strength of the polymer by the use of a filler material intimately mixed with the polymer to form a composite material. These composites have, however, failed due to an increase in the coefficients of friction. These higher coefficients of friction are due to the wear process exposing the filler material so that the mating surface no longer rides on a true polymer interface. Another technique, which has been used to attempt to increase the yield strength of the polymer is the incorporation of a woven metal screen to form a composite. This also fails as the friction between the metal threads is insufficient to prevent yielding of both the polymer and the lateral movement of the screen wires across each other. Further, the yielding of the screen wire can be preferential depending on the direction of the shear force and the "lay" or "bias" of the woven screen. Attempts to further increase the strength of the composite by adhesively bonding the screen to a metal backing has failed as the area open to bonding is small due to the roundness of the screen wires and the fill of the polymer in the mesh.
Accordingly, among the objectives of the present invention are to provide a positive displacement pump or motor which has a non-rolling element saddle type bearing of increased load capacity; which would withstand the normal forces on the bearing on the pump or motor; and which can be relatively easily manufactured; and bearings which can be utilized in other force conditions involving radial and axial loads.
In accordance with the invention, a bearing comprising a body of polymeric material and a reinforcing member embedded in the body and having a plurality of perforations throughout which are affixed in the reinforcing member. The polymeric material extends through the perforations. The bearing may have various configurations. The reinforcing member may comprise a thin metal sheet having perforations therein, a woven metal body defining the perforations, or adjacent woven metal bodies each having perforations. In one form, a backing member is adhered to one side of said reinforcing member. Where a thin metal sheet is used, it has a roughened surface finish at the interface with the plastic body.